An engine combusts a mixture of fuel and air to generate a mechanical power output, along with a flow of hot exhaust gases. A charged engine includes one or more compressors that are driven to compress combustion air entering the engine. By forcing compressed air into the engine, more air becomes available for combustion than could otherwise be drawn into the engine by motion of the engine's pistons. This increased supply of air allows for a corresponding increase in fueling, resulting in increased power output. A charged engine typically produces more power than the same engine without charging.
An engine can be charged in different ways. For example, the engine can be turbocharged, wherein a turbine is driven by hot exhaust gases produced by the engine and connected to mechanically drive the compressor. In another example, the compressor can be mechanically connected to a crankshaft of the engine and directly driven by the engine. When the compressor is mechanically connected to the crankshaft of an engine, the engine is said to be supercharged. In some situations, the engine can be both turbocharged and supercharged.
It may be possible for a compressor to supply too much air to an engine. For example, at low engine loads, a compressor can actually supply enough air to overly cool the engine and thereby reduce combustion efficiency and/or increase exhaust emissions. In addition, when the engine is supplied with gaseous fuel at low load settings, combustion can be quenched by the excess air.
One attempt to address these problems is disclosed in U.S. Pat. No. 5,079,921 of McCandless et al. that issued on Jan. 14, 1992 (“the '921 patent”). Specifically, the '921 patent discloses an exhaust backpressure control system having a valve in the exhaust outlet of a turbocharger. The valve is controlled by a microcomputer to close and restrict exhaust flow during startup of an engine. By restricting the exhaust flow, backpressure and friction are increased within the engine to thereby cause the engine to work harder and warm up quicker than would otherwise be possible. The valve is moved by the microcomputer as a function of an engine coolant temperature, engine speed, engine fuel consumption, and actual backpressure.
Although the exhaust backpressure control system of the '921 patent may be adequate in some situations, it may lack applicability to dual-fuel systems and/or to systems having a hybrid charged system (i.e., a system that is both turbocharged and supercharged).
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.